The present invention relates to an inkjet printer and, in particular, to an inkjet printer using ink that is cured when exposed to ultraviolet rays.
In recent years, inkjet recording method has been employed in the field of special printing for photographs, various types of prints, markings and color filters for its capability of creating an image more simply and inexpensively than the gravure printing method. In the inkjet recording method, in particular, excellent image quality comparable to that of a silver halide photograph can be provided by a combination among: an inkjet printer based on the ink-jet recording method capable of ejecting and controlling minute dots; ink characterized by improved color reproduction area, durability and ejection properties; and special paper characterized by drastic improvement in ink absorbency, color developing properties of the coloring material and surface gloss.
The prior art inkjet printer is based on a line method where image recording is performed by the ink ejected from the line head where a plurality of ink outlets arranged in the scanning direction orthogonal to the transport direction are formed on the recording medium transported in the direction of transport; and a serial method where the recording head mounted on a carriage is moved in the scanning direction and ink is ejected from the ink outlet of the recording head during the traveling of the recording head, whereby an image is recorded.
Further, the inkjet printer can be classified according to the type of ink. To be more specific, the prior art ink-jet printer is available in a phase-change inkjet method where solid wax ink is used in the room temperature; a solvent based inkjet method using ink mainly consisting of a quick-dry organic solvent; and an ultraviolet cure type ink-jet method using ultraviolet cure ink which is cured when exposed to ultraviolet rays. Among them, the ultraviolet cure type inkjet method is relatively odorless as compared with other recording methods, and allows recording on the recording medium that has no quick drying properties or high ink absorbency, in addition to special-purpose paper. (See Patent Document 1, for example).
Incidentally, the inkjet printer may fail to eject ink properly if ink is deposited on the nozzle surface of the recording head with ink outlets arranged thereon. Especially in the inkjet printer based on ultraviolet cure ink, ink is cured when exposed to ultraviolet rays. Ultraviolet rays are applied to the ink deposited on the nozzle surface of the recording head, and ink is cured, with the result that ink ejection failure occurs. Such a trouble occurs more frequently in the inkjet printer using ultraviolet cure ink than in inkjet printer using other methods.
To solve this problem in the prior art, a light trap consisting of a concave member opening toward the recording medium, for example, is arranged between the recording head and ultraviolet ray irradiation apparatus. This light trap receives the reflected light produced when the ultraviolet rays applied from the ultraviolet ray irradiation apparatus hits the recording medium or platen, whereby the reflected light is cut off and the recording head is prevented from being exposed to ultraviolet rays.
In the ultraviolet cure type inkjet printer, ink is deposited on the surface of the nozzle upper plate of the recording head where ink outlets are arranged. This makes it difficult to remove the ink by wiping the recording head thereafter, with the result that correct ink ejection operation fails. Further, if ultraviolet rays are applied to the ink inside the nozzle that is not ejecting ink, ink will be cured and the nozzle will be clogged with ink; this leads to a failure in restarting ink ejection. To solve this problem, water-shedding treatment for shedding ink to prevent it from being deposited is provided on the surface of the nozzle upper plate. (See Patent Document 2, for example). Further, idle ejecting has been performed frequently by interrupting the printing operation.
In addition, a technique has been disclosed to provide water-shedding treatment to the protection upper plate for protecting the nozzle upper plate. (See Patent Document 3, for example). A further technique is disclosed, in which a level difference is provided between the surface of the nozzle upper plate and that of the protection upper plate, thereby reducing the amount of light applied to the nozzle upper plate. (See Patent Document 4, for example). A still further technique is disclosed wherein the material used for water-shedding treatment is selected with reference to the sliding speed. (See Patent Document 5, for example).
[Patent Document 1] Official Gazette of Japanese Patent Tokkai 2001-310454
[Patent Document 2] Official Gazette of Japanese Patent 3188816
[Patent Document 3] Official Gazette of Japanese Patent 3457458
[Patent Document 4] Official Gazette of Japanese Patent Tokkai 2002-79666
[Patent Document 5] Official Gazette of Japanese Patent Tokkai 2003-266702